Since KDE 1.0, KDE supports the legacy X11R4 and ICCCM session management protocols. It will restart with the specified command all legacy applications that define the <tt>WM_COMMAND</tt> property or support the <tt>WM_SAVE_YOURSELF</tt> protocol. It will also restore the window geometries on a best effort basis.

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are supported. Legacy applications that define the <tt>WM_COMMAND</tt>

+

−

property or support the <tt>WM_SAVE_YOURSELF</tt> protocol will be restarted

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with the specified command. The window geometries will be restored on a best

for you, that your application can utilize to store session specific data.

+

for you, that your application can use to store session specific data.

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Please read the respective class documentation, especially the one of

+

Please read the class documentation, especially the one of

[http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow], for a detailed interface description. With the advanced

[http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow], for a detailed interface description. With the advanced

functionality in [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow], it's really just a matter of a few lines to get even a multi-window application to retains its state between

functionality in [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow], it's really just a matter of a few lines to get even a multi-window application to retains its state between

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==Implementing session management in your application==

==Implementing session management in your application==

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Here's just a brief overview how things are done. Again, see the

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Here's just a brief overview how you can add session management to your application. Again, see the class documentation for details.

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respective class documentation for details.

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Implementing session management in KDE is easy. If your main window inherits from [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow], you have just 2 things to do:

Implementing session management in KDE is easy. If your main window inherits from [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow], you have just 2 things to do:

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===Reimplement some virtual functions of KMainWindow===

===Reimplement some virtual functions of KMainWindow===

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[http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow] will save its position, geometry and positions of toolbars and menubar on logout.

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[http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow] will automatically save its position, geometry and positions of toolbars and menu bar on logout - and restore it on the next startup.

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* To warn the user that the application or some windows have unsaved data on close or logout (for example: show a dialog with the buttons "Save changes" and "Discard changes"), reimplement [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#f8c5708414be62f259114b0453ef8432 queryClose()].

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* To save additional data, reimplement [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#4c7a6c395eec0bb245cd9ad6c884f897 saveProperties()]. (For a text editor, that would be the loaded files, for example.) Note that no user interaction is allowed in this function! For example, you may not display any dialog!

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For every other data that your application needs to restore a session, you have to write the code for saving and restoring yourself. However, [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow] makes this task easy. You can just re-implement the following functions:

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* To read the additional data again on next login, reimplement [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#c8d0d64ed5b309ba1da410423120d0a6 readProperties()].

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* [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#4c7a6c395eec0bb245cd9ad6c884f897 saveProperties()]: This function is called only when the session manager closes the application (and not when the user closes the application). To save the data that you need to restore the session, reimplement this function. (For a text editor that would be the list of loaded files) Note that you may not do any user interaction in this function! (For example, you may not display any dialog!)

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These functions are called automatically by [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow] respectively by the session manager. Note that it is not determined if [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#4c7a6c395eec0bb245cd9ad6c884f897 saveProperties()] is called before or after [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#f8c5708414be62f259114b0453ef8432 queryClose()]! Please read documentation of the respective functions before reimplementing them.

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* [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#c8d0d64ed5b309ba1da410423120d0a6 readProperties()]: To read the data again on next login, reimplement this function.

+

+

Furthermore, the function [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#f8c5708414be62f259114b0453ef8432 queryClose()] could be interesting for you. This function is called ''always'' before the window is closed, either by the user or indirectly by the session manager. ''(Note that this is not the case for a call of KApplication::quit() because this function will exit the event loop without causing a close event for the main windows. It will even not destroy them.)'' Typically, here you can warn the user that the application or some windows have unsaved data on close or logout (example: show a dialog with the buttons "Save changes" and "Discard changes"). However, for session management it isn't nice to need a user interaction before closing, so you better avoid this. Note that it is not determined if [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#4c7a6c395eec0bb245cd9ad6c884f897 saveProperties()] is called before or after [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#f8c5708414be62f259114b0453ef8432 queryClose()]!

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To save your application-wide properties (data that is only needed once per application, and not for each main window) reimplement [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#cf811d77a3acdcf2b61f8826429615a7 saveGlobalProperties()] and it's counterpart [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#2d4da4f305f00e8a5c94f5b978334231 readGlobalProperties]. Normally, you don't need these functions.

+

''To save your application-wide properties (data that is only needed once per application, and not for each main window instance) reimplement [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#cf811d77a3acdcf2b61f8826429615a7 saveGlobalProperties()] and it's counterpart [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#2d4da4f305f00e8a5c94f5b978334231 readGlobalProperties]. Normally, you don't need these functions.''

===Add session management support to your main() function===

===Add session management support to your main() function===

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While [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#4c7a6c395eec0bb245cd9ad6c884f897 KMainWindow::saveProperties()] and [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#f8c5708414be62f259114b0453ef8432 KMainWindow::queryClose()] will work out of the box, [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#c8d0d64ed5b309ba1da410423120d0a6 KMainWindow::readProperties()] will not. You have to add some code to your main() function to implement session restoring.

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While [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#4c7a6c395eec0bb245cd9ad6c884f897 KMainWindow::saveProperties()] (and [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#f8c5708414be62f259114b0453ef8432 KMainWindow::queryClose()]) will be called automatically, [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#c8d0d64ed5b309ba1da410423120d0a6 KMainWindow::readProperties()] will not. You have to add some code to your main() function to add session restoring.

Imagine you have an

Imagine you have an

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[http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKXmlGuiWindow.html KXmlGuiWindow], which inherits from

[http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKXmlGuiWindow.html KXmlGuiWindow], which inherits from

[http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow]). In your main() function, you would then create/restore the

[http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow]). In your main() function, you would then create/restore the

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application windows with something like:

+

application windows with something like this:

−

<code cppqt>

+

<syntaxhighlight lang="cpp-qt">

KApplication app;

KApplication app;

if ( app.isSessionRestored() ) {

if ( app.isSessionRestored() ) {

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} else {

} else {

// create default application as usual

// create default application as usual

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// for example:

+

// example:

MyWindow * window = new MyWindow();

MyWindow * window = new MyWindow();

−

// # will be replaced with numbers that are guaranteed

+

// The function will replace '#' with numbers that are

−

// to be unique in the application:

+

// unique within the application:

window->setObjectName("MyWindow#");

window->setObjectName("MyWindow#");

window->show();

window->show();

}

}

return app.exec();

return app.exec();

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</code>

+

</syntaxhighlight>

[http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/kmainwindow_8h.html#88ce427e39f425eefa5a94d746eb2bed kRestoreMainWindows<>()] will create (on the heap) as many instances of your main windows as have existed in the last session and call [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#46e01bd1aa6d488f1be2a5010030efb2 KMainWindow::restore()] with the correct arguments. Note that also QWidget::show() is called implicitly.

[http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/kmainwindow_8h.html#88ce427e39f425eefa5a94d746eb2bed kRestoreMainWindows<>()] will create (on the heap) as many instances of your main windows as have existed in the last session and call [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html#46e01bd1aa6d488f1be2a5010030efb2 KMainWindow::restore()] with the correct arguments. Note that also QWidget::show() is called implicitly.

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About setObjectName("MyWindow#"): For session management and window management to work properly, all main windows in the application should have a different name. If you don't do it, KMainWindow will create a unique name, but it's recommended to explicitly pass a window name that will also describe the type of the window. If there can be several windows of the same type, append '#' (hash) to the name, and KMainWindow will replace it with numbers to make the names unique. For example, for a mail client which has one main window showing the mails and folders, and which can also have one or more windows for composing mails, the name for the folders window should be e.g. "mainwindow" and for the composer windows "composer#".

About setObjectName("MyWindow#"): For session management and window management to work properly, all main windows in the application should have a different name. If you don't do it, KMainWindow will create a unique name, but it's recommended to explicitly pass a window name that will also describe the type of the window. If there can be several windows of the same type, append '#' (hash) to the name, and KMainWindow will replace it with numbers to make the names unique. For example, for a mail client which has one main window showing the mails and folders, and which can also have one or more windows for composing mails, the name for the folders window should be e.g. "mainwindow" and for the composer windows "composer#".

−

With this you can easily restore all toplevel windows of your application.

+

With this you can easily restore all top-level windows of your application.

−

It is also possible to restore different types of toplevel windows (each

+

It is also possible to restore different types of top-level windows (each

derived from [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow], of course) within one application. Imagine you have three classes of main windows: childMW1, childMW2 and childMW3:

derived from [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/classKMainWindow.html KMainWindow], of course) within one application. Imagine you have three classes of main windows: childMW1, childMW2 and childMW3:

−

<code cppqt>

+

<syntaxhighlight lang="cpp-qt">

KApplication app;

KApplication app;

if ( app.isSessionRestored() ) {

if ( app.isSessionRestored() ) {

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} else {

} else {

// create default application as usual

// create default application as usual

−

// for example:

+

// example:

childMW1* window1 = new childMW1();

childMW1* window1 = new childMW1();

childMW2* window2 = new childMW2();

childMW2* window2 = new childMW2();

childMW3* window3 = new childMW3();

childMW3* window3 = new childMW3();

−

// # will be replaced with numbers that are guaranteed

+

// The function will replace '#' with numbers that are

−

// to be unique in the application:

+

// unique within the application:

window1->setObjectName("type1mainWindow#");

window1->setObjectName("type1mainWindow#");

window2->setObjectName("type2mainWindow#");

window2->setObjectName("type2mainWindow#");

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}

}

return app.exec();

return app.exec();

−

</code>

+

</syntaxhighlight>

−

Currently, the [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/kmainwindow_8h.html#88ce427e39f425eefa5a94d746eb2bed kRestoreMainWindows<>()] template functions are provided for up to three template arguments.

+

Currently, kdelibs provides the [http://api.kde.org/4.x-api/kdelibs-apidocs/kdeui/html/kmainwindow_8h.html#88ce427e39f425eefa5a94d746eb2bed kRestoreMainWindows<>()] template functions for up to three template arguments.

==Appendix: Architecture of the KDE session manager==

==Appendix: Architecture of the KDE session manager==

−

The session management server in KDE is called '''ksmserver''' and it is

+

The name of the session management server in KDE is '''ksmserver''' and it is

part of the '''kdebase''' package. The server interacts with the KDE window

part of the '''kdebase''' package. The server interacts with the KDE window

manager '''kwin''' to save and restore the window geometries and to perform

manager '''kwin''' to save and restore the window geometries and to perform

Since KDE 1.0, KDE supports the legacy X11R4 and ICCCM session management protocols. It will restart with the specified command all legacy applications that define the WM_COMMAND property or support the WM_SAVE_YOURSELF protocol. It will also restore the window geometries on a best effort basis.

Since KDE 2.0, KDE also supports the standard X11R6 session management protocol XSMP and uses it. You can download the official documentation of the
standard from the X Consortium's FTP server
ftp.x.org. Unlike the legacy protocols, the new X11R6
session management gives a chance to save application
dependent settings when you log out. A text
editor, for instance, would save the names of the loaded files and would
reload them when you log in again. Another major advantage of the new
protocol is the support for a clean and safe logout procedure even if the
users decides not to restore the session next time. The protocol gives
applications the possibility to interact with the user if they are in
danger to lose some data, and to cancel the shutdown process if necessary.

Please read the class documentation, especially the one of
KMainWindow, for a detailed interface description. With the advanced
functionality in KMainWindow, it's really just a matter of a few lines to get even a multi-window application to retains its state between
different user sessions.

KMainWindow will automatically save its position, geometry and positions of toolbars and menu bar on logout - and restore it on the next startup.

For every other data that your application needs to restore a session, you have to write the code for saving and restoring yourself. However, KMainWindow makes this task easy. You can just re-implement the following functions:

saveProperties(): This function is called only when the session manager closes the application (and not when the user closes the application). To save the data that you need to restore the session, reimplement this function. (For a text editor that would be the list of loaded files) Note that you may not do any user interaction in this function! (For example, you may not display any dialog!)

readProperties(): To read the data again on next login, reimplement this function.

Furthermore, the function queryClose() could be interesting for you. This function is called always before the window is closed, either by the user or indirectly by the session manager. (Note that this is not the case for a call of KApplication::quit() because this function will exit the event loop without causing a close event for the main windows. It will even not destroy them.) Typically, here you can warn the user that the application or some windows have unsaved data on close or logout (example: show a dialog with the buttons "Save changes" and "Discard changes"). However, for session management it isn't nice to need a user interaction before closing, so you better avoid this. Note that it is not determined if saveProperties() is called before or after queryClose()!

To save your application-wide properties (data that is only needed once per application, and not for each main window instance) reimplement saveGlobalProperties() and it's counterpart readGlobalProperties. Normally, you don't need these functions.

Imagine you have an
application with a main window MyWindow inherited from
KMainWindow (or from
KXmlGuiWindow, which inherits from
KMainWindow). In your main() function, you would then create/restore the
application windows with something like this:

kRestoreMainWindows<>() will create (on the heap) as many instances of your main windows as have existed in the last session and call KMainWindow::restore() with the correct arguments. Note that also QWidget::show() is called implicitly.

About setObjectName("MyWindow#"): For session management and window management to work properly, all main windows in the application should have a different name. If you don't do it, KMainWindow will create a unique name, but it's recommended to explicitly pass a window name that will also describe the type of the window. If there can be several windows of the same type, append '#' (hash) to the name, and KMainWindow will replace it with numbers to make the names unique. For example, for a mail client which has one main window showing the mails and folders, and which can also have one or more windows for composing mails, the name for the folders window should be e.g. "mainwindow" and for the composer windows "composer#".

With this you can easily restore all top-level windows of your application.

It is also possible to restore different types of top-level windows (each
derived from KMainWindow, of course) within one application. Imagine you have three classes of main windows: childMW1, childMW2 and childMW3:

The name of the session management server in KDE is ksmserver and it is
part of the kdebase package. The server interacts with the KDE window
manager kwin to save and restore the window geometries and to perform
legacy session management. To make session management work, ksmserver
has to be started as last process of the X login procedure. This happens
automatically at the end of the startkde script.